/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.reflect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterables.transform;
import static java.util.Objects.requireNonNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Objects;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;

import java.io.Serializable;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.GenericDeclaration;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.security.AccessControlException;
import java.util.Arrays;
import java.util.Collection;
import java.util.Map.Entry;
import java.util.concurrent.atomic.AtomicReference;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Utilities for working with {@link Type}.
 *
 * @author Ben Yu
 */
@ElementTypesAreNonnullByDefault
final class Types
{

    /**
     * Class#toString without the "class " and "interface " prefixes
     */
    private static final Joiner COMMA_JOINER = Joiner.on(", ").useForNull("null");

    /**
     * Returns the array type of {@code componentType}.
     */
    static Type newArrayType(Type componentType)
    {
        if (componentType instanceof WildcardType)
        {
            WildcardType wildcard = (WildcardType) componentType;
            Type[] lowerBounds = wildcard.getLowerBounds();
            checkArgument(lowerBounds.length <= 1, "Wildcard cannot have more than one lower bounds.");
            if (lowerBounds.length == 1)
            {
                return supertypeOf(newArrayType(lowerBounds[0]));
            }
            else
            {
                Type[] upperBounds = wildcard.getUpperBounds();
                checkArgument(upperBounds.length == 1, "Wildcard should have only one upper bound.");
                return subtypeOf(newArrayType(upperBounds[0]));
            }
        }
        return JavaVersion.CURRENT.newArrayType(componentType);
    }

    /**
     * Returns a type where {@code rawType} is parameterized by {@code arguments} and is owned by
     * {@code ownerType}.
     */
    static ParameterizedType newParameterizedTypeWithOwner(
            @CheckForNull Type ownerType, Class<?> rawType, Type... arguments)
    {
        if (ownerType == null)
        {
            return newParameterizedType(rawType, arguments);
        }
        // ParameterizedTypeImpl constructor already checks, but we want to throw NPE before IAE
        checkNotNull(arguments);
        checkArgument(rawType.getEnclosingClass() != null, "Owner type for unenclosed %s", rawType);
        return new ParameterizedTypeImpl(ownerType, rawType, arguments);
    }

    /**
     * Returns a type where {@code rawType} is parameterized by {@code arguments}.
     */
    static ParameterizedType newParameterizedType(Class<?> rawType, Type... arguments)
    {
        return new ParameterizedTypeImpl(
                ClassOwnership.JVM_BEHAVIOR.getOwnerType(rawType), rawType, arguments);
    }

    /**
     * Decides what owner type to use for constructing {@link ParameterizedType} from a raw class.
     */
    private enum ClassOwnership
    {
        OWNED_BY_ENCLOSING_CLASS
                {
                    @Override
                    @CheckForNull
                    Class<?> getOwnerType(Class<?> rawType)
                    {
                        return rawType.getEnclosingClass();
                    }
                },
        LOCAL_CLASS_HAS_NO_OWNER
                {
                    @Override
                    @CheckForNull
                    Class<?> getOwnerType(Class<?> rawType)
                    {
                        if (rawType.isLocalClass())
                        {
                            return null;
                        }
                        else
                        {
                            return rawType.getEnclosingClass();
                        }
                    }
                };

        @CheckForNull
        abstract Class<?> getOwnerType(Class<?> rawType);

        static final ClassOwnership JVM_BEHAVIOR = detectJvmBehavior();

        private static ClassOwnership detectJvmBehavior()
        {
            class LocalClass<T>
            {
            }
            Class<?> subclass = new LocalClass<String>()
            {
            }.getClass();
            // requireNonNull is safe because we're examining a type that's known to have a superclass.
            ParameterizedType parameterizedType =
                    requireNonNull((ParameterizedType) subclass.getGenericSuperclass());
            for (ClassOwnership behavior : ClassOwnership.values())
            {
                if (behavior.getOwnerType(LocalClass.class) == parameterizedType.getOwnerType())
                {
                    return behavior;
                }
            }
            throw new AssertionError();
        }
    }

    /**
     * Returns a new {@link TypeVariable} that belongs to {@code declaration} with {@code name} and
     * {@code bounds}.
     */
    static <D extends GenericDeclaration> TypeVariable<D> newArtificialTypeVariable(
            D declaration, String name, Type... bounds)
    {
        return newTypeVariableImpl(
                declaration, name, (bounds.length == 0) ? new Type[]{Object.class} : bounds);
    }

    /**
     * Returns a new {@link WildcardType} with {@code upperBound}.
     */
    @VisibleForTesting
    static WildcardType subtypeOf(Type upperBound)
    {
        return new WildcardTypeImpl(new Type[0], new Type[]{upperBound});
    }

    /**
     * Returns a new {@link WildcardType} with {@code lowerBound}.
     */
    @VisibleForTesting
    static WildcardType supertypeOf(Type lowerBound)
    {
        return new WildcardTypeImpl(new Type[]{lowerBound}, new Type[]{Object.class});
    }

    /**
     * Returns human readable string representation of {@code type}.
     *
     * <p>The format is subject to change.
     */
    static String toString(Type type)
    {
        return (type instanceof Class) ? ((Class<?>) type).getName() : type.toString();
    }

    @CheckForNull
    static Type getComponentType(Type type)
    {
        checkNotNull(type);
        AtomicReference<@Nullable Type> result = new AtomicReference<>();
        new TypeVisitor()
        {
            @Override
            void visitTypeVariable(TypeVariable<?> t)
            {
                result.set(subtypeOfComponentType(t.getBounds()));
            }

            @Override
            void visitWildcardType(WildcardType t)
            {
                result.set(subtypeOfComponentType(t.getUpperBounds()));
            }

            @Override
            void visitGenericArrayType(GenericArrayType t)
            {
                result.set(t.getGenericComponentType());
            }

            @Override
            void visitClass(Class<?> t)
            {
                result.set(t.getComponentType());
            }
        }.visit(type);
        return result.get();
    }

    /**
     * Returns {@code ? extends X} if any of {@code bounds} is a subtype of {@code X[]}; or null
     * otherwise.
     */
    @CheckForNull
    private static Type subtypeOfComponentType(Type[] bounds)
    {
        for (Type bound : bounds)
        {
            Type componentType = getComponentType(bound);
            if (componentType != null)
            {
                // Only the first bound can be a class or array.
                // Bounds after the first can only be interfaces.
                if (componentType instanceof Class)
                {
                    Class<?> componentClass = (Class<?>) componentType;
                    if (componentClass.isPrimitive())
                    {
                        return componentClass;
                    }
                }
                return subtypeOf(componentType);
            }
        }
        return null;
    }

    private static final class GenericArrayTypeImpl implements GenericArrayType, Serializable
    {

        private final Type componentType;

        GenericArrayTypeImpl(Type componentType)
        {
            this.componentType = JavaVersion.CURRENT.usedInGenericType(componentType);
        }

        @Override
        public Type getGenericComponentType()
        {
            return componentType;
        }

        @Override
        public String toString()
        {
            return Types.toString(componentType) + "[]";
        }

        @Override
        public int hashCode()
        {
            return componentType.hashCode();
        }

        @Override
        public boolean equals(@CheckForNull Object obj)
        {
            if (obj instanceof GenericArrayType)
            {
                GenericArrayType that = (GenericArrayType) obj;
                return Objects.equal(getGenericComponentType(), that.getGenericComponentType());
            }
            return false;
        }

        private static final long serialVersionUID = 0;
    }

    private static final class ParameterizedTypeImpl implements ParameterizedType, Serializable
    {

        @CheckForNull
        private final Type ownerType;
        private final ImmutableList<Type> argumentsList;
        private final Class<?> rawType;

        ParameterizedTypeImpl(@CheckForNull Type ownerType, Class<?> rawType, Type[] typeArguments)
        {
            checkNotNull(rawType);
            checkArgument(typeArguments.length == rawType.getTypeParameters().length);
            disallowPrimitiveType(typeArguments, "type parameter");
            this.ownerType = ownerType;
            this.rawType = rawType;
            this.argumentsList = JavaVersion.CURRENT.usedInGenericType(typeArguments);
        }

        @Override
        public Type[] getActualTypeArguments()
        {
            return toArray(argumentsList);
        }

        @Override
        public Type getRawType()
        {
            return rawType;
        }

        @Override
        @CheckForNull
        public Type getOwnerType()
        {
            return ownerType;
        }

        @Override
        public String toString()
        {
            StringBuilder builder = new StringBuilder();
            if (ownerType != null && JavaVersion.CURRENT.jdkTypeDuplicatesOwnerName())
            {
                builder.append(JavaVersion.CURRENT.typeName(ownerType)).append('.');
            }
            return builder
                    .append(rawType.getName())
                    .append('<')
                    .append(COMMA_JOINER.join(transform(argumentsList, JavaVersion.CURRENT::typeName)))
                    .append('>')
                    .toString();
        }

        @Override
        public int hashCode()
        {
            return (ownerType == null ? 0 : ownerType.hashCode())
                    ^ argumentsList.hashCode()
                    ^ rawType.hashCode();
        }

        @Override
        public boolean equals(@CheckForNull Object other)
        {
            if (!(other instanceof ParameterizedType))
            {
                return false;
            }
            ParameterizedType that = (ParameterizedType) other;
            return getRawType().equals(that.getRawType())
                    && Objects.equal(getOwnerType(), that.getOwnerType())
                    && Arrays.equals(getActualTypeArguments(), that.getActualTypeArguments());
        }

        private static final long serialVersionUID = 0;
    }

    private static <D extends GenericDeclaration> TypeVariable<D> newTypeVariableImpl(
            D genericDeclaration, String name, Type[] bounds)
    {
        TypeVariableImpl<D> typeVariableImpl = new TypeVariableImpl<>(genericDeclaration, name, bounds);
        @SuppressWarnings("unchecked")
        TypeVariable<D> typeVariable =
                Reflection.newProxy(
                        TypeVariable.class, new TypeVariableInvocationHandler(typeVariableImpl));
        return typeVariable;
    }

    /**
     * Invocation handler to work around a compatibility problem between Java 7 and Java 8.
     *
     * <p>Java 8 introduced a new method {@code getAnnotatedBounds()} in the {@link TypeVariable}
     * interface, whose return type {@code AnnotatedType[]} is also new in Java 8. That means that we
     * cannot implement that interface in source code in a way that will compile on both Java 7 and
     * Java 8. If we include the {@code getAnnotatedBounds()} method then its return type means it
     * won't compile on Java 7, while if we don't include the method then the compiler will complain
     * that an abstract method is unimplemented. So instead we use a dynamic proxy to get an
     * implementation. If the method being called on the {@code TypeVariable} instance has the same
     * name as one of the public methods of {@link TypeVariableImpl}, the proxy calls the same method
     * on its instance of {@code TypeVariableImpl}. Otherwise it throws {@link
     * UnsupportedOperationException}; this should only apply to {@code getAnnotatedBounds()}. This
     * does mean that users on Java 8 who obtain an instance of {@code TypeVariable} from {@link
     * TypeResolver#resolveType} will not be able to call {@code getAnnotatedBounds()} on it, but that
     * should hopefully be rare.
     *
     * <p>TODO(b/147144588): We are currently also missing the methods inherited from {@link
     * AnnotatedElement}, which {@code TypeVariable} began to extend only in Java 8. Those methods
     * refer only to types present in Java 7, so we could implement them in {@code TypeVariableImpl}
     * today. (We could probably then make {@code TypeVariableImpl} implement {@code AnnotatedElement}
     * so that we get partial compile-time checking.)
     *
     * <p>This workaround should be removed at a distant future time when we no longer support Java
     * versions earlier than 8.
     */
    private static final class TypeVariableInvocationHandler implements InvocationHandler
    {
        private static final ImmutableMap<String, Method> typeVariableMethods;

        static
        {
            ImmutableMap.Builder<String, Method> builder = ImmutableMap.builder();
            for (Method method : TypeVariableImpl.class.getMethods())
            {
                if (method.getDeclaringClass().equals(TypeVariableImpl.class))
                {
                    try
                    {
                        method.setAccessible(true);
                    }
                    catch (AccessControlException e)
                    {
                        // OK: the method is accessible to us anyway. The setAccessible call is only for
                        // unusual execution environments where that might not be true.
                    }
                    builder.put(method.getName(), method);
                }
            }
            typeVariableMethods = builder.build();
        }

        private final TypeVariableImpl<?> typeVariableImpl;

        TypeVariableInvocationHandler(TypeVariableImpl<?> typeVariableImpl)
        {
            this.typeVariableImpl = typeVariableImpl;
        }

        @Override
        @CheckForNull
        public Object invoke(Object proxy, Method method, @CheckForNull @Nullable Object[] args)
                throws Throwable
        {
            String methodName = method.getName();
            Method typeVariableMethod = typeVariableMethods.get(methodName);
            if (typeVariableMethod == null)
            {
                throw new UnsupportedOperationException(methodName);
            }
            else
            {
                try
                {
                    return typeVariableMethod.invoke(typeVariableImpl, args);
                }
                catch (InvocationTargetException e)
                {
                    throw e.getCause();
                }
            }
        }
    }

    private static final class TypeVariableImpl<D extends GenericDeclaration>
    {

        private final D genericDeclaration;
        private final String name;
        private final ImmutableList<Type> bounds;

        TypeVariableImpl(D genericDeclaration, String name, Type[] bounds)
        {
            disallowPrimitiveType(bounds, "bound for type variable");
            this.genericDeclaration = checkNotNull(genericDeclaration);
            this.name = checkNotNull(name);
            this.bounds = ImmutableList.copyOf(bounds);
        }

        public Type[] getBounds()
        {
            return toArray(bounds);
        }

        public D getGenericDeclaration()
        {
            return genericDeclaration;
        }

        public String getName()
        {
            return name;
        }

        public String getTypeName()
        {
            return name;
        }

        @Override
        public String toString()
        {
            return name;
        }

        @Override
        public int hashCode()
        {
            return genericDeclaration.hashCode() ^ name.hashCode();
        }

        @Override
        public boolean equals(@CheckForNull Object obj)
        {
            if (NativeTypeVariableEquals.NATIVE_TYPE_VARIABLE_ONLY)
            {
                // equal only to our TypeVariable implementation with identical bounds
                if (obj != null
                        && Proxy.isProxyClass(obj.getClass())
                        && Proxy.getInvocationHandler(obj) instanceof TypeVariableInvocationHandler)
                {
                    TypeVariableInvocationHandler typeVariableInvocationHandler =
                            (TypeVariableInvocationHandler) Proxy.getInvocationHandler(obj);
                    TypeVariableImpl<?> that = typeVariableInvocationHandler.typeVariableImpl;
                    return name.equals(that.getName())
                            && genericDeclaration.equals(that.getGenericDeclaration())
                            && bounds.equals(that.bounds);
                }
                return false;
            }
            else
            {
                // equal to any TypeVariable implementation regardless of bounds
                if (obj instanceof TypeVariable)
                {
                    TypeVariable<?> that = (TypeVariable<?>) obj;
                    return name.equals(that.getName())
                            && genericDeclaration.equals(that.getGenericDeclaration());
                }
                return false;
            }
        }
    }

    static final class WildcardTypeImpl implements WildcardType, Serializable
    {

        private final ImmutableList<Type> lowerBounds;
        private final ImmutableList<Type> upperBounds;

        WildcardTypeImpl(Type[] lowerBounds, Type[] upperBounds)
        {
            disallowPrimitiveType(lowerBounds, "lower bound for wildcard");
            disallowPrimitiveType(upperBounds, "upper bound for wildcard");
            this.lowerBounds = JavaVersion.CURRENT.usedInGenericType(lowerBounds);
            this.upperBounds = JavaVersion.CURRENT.usedInGenericType(upperBounds);
        }

        @Override
        public Type[] getLowerBounds()
        {
            return toArray(lowerBounds);
        }

        @Override
        public Type[] getUpperBounds()
        {
            return toArray(upperBounds);
        }

        @Override
        public boolean equals(@CheckForNull Object obj)
        {
            if (obj instanceof WildcardType)
            {
                WildcardType that = (WildcardType) obj;
                return lowerBounds.equals(Arrays.asList(that.getLowerBounds()))
                        && upperBounds.equals(Arrays.asList(that.getUpperBounds()));
            }
            return false;
        }

        @Override
        public int hashCode()
        {
            return lowerBounds.hashCode() ^ upperBounds.hashCode();
        }

        @Override
        public String toString()
        {
            StringBuilder builder = new StringBuilder("?");
            for (Type lowerBound : lowerBounds)
            {
                builder.append(" super ").append(JavaVersion.CURRENT.typeName(lowerBound));
            }
            for (Type upperBound : filterUpperBounds(upperBounds))
            {
                builder.append(" extends ").append(JavaVersion.CURRENT.typeName(upperBound));
            }
            return builder.toString();
        }

        private static final long serialVersionUID = 0;
    }

    private static Type[] toArray(Collection<Type> types)
    {
        return types.toArray(new Type[0]);
    }

    private static Iterable<Type> filterUpperBounds(Iterable<Type> bounds)
    {
        return Iterables.filter(bounds, Predicates.not(Predicates.<Type>equalTo(Object.class)));
    }

    private static void disallowPrimitiveType(Type[] types, String usedAs)
    {
        for (Type type : types)
        {
            if (type instanceof Class)
            {
                Class<?> cls = (Class<?>) type;
                checkArgument(!cls.isPrimitive(), "Primitive type '%s' used as %s", cls, usedAs);
            }
        }
    }

    /**
     * Returns the {@code Class} object of arrays with {@code componentType}.
     */
    static Class<?> getArrayClass(Class<?> componentType)
    {
        // TODO(user): This is not the most efficient way to handle generic
        // arrays, but is there another way to extract the array class in a
        // non-hacky way (i.e. using String value class names- "[L...")?
        return Array.newInstance(componentType, 0).getClass();
    }

    // TODO(benyu): Once behavior is the same for all Java versions we support, delete this.
    enum JavaVersion
    {
        JAVA6
                {
                    @Override
                    GenericArrayType newArrayType(Type componentType)
                    {
                        return new GenericArrayTypeImpl(componentType);
                    }

                    @Override
                    Type usedInGenericType(Type type)
                    {
                        checkNotNull(type);
                        if (type instanceof Class)
                        {
                            Class<?> cls = (Class<?>) type;
                            if (cls.isArray())
                            {
                                return new GenericArrayTypeImpl(cls.getComponentType());
                            }
                        }
                        return type;
                    }
                },
        JAVA7
                {
                    @Override
                    Type newArrayType(Type componentType)
                    {
                        if (componentType instanceof Class)
                        {
                            return getArrayClass((Class<?>) componentType);
                        }
                        else
                        {
                            return new GenericArrayTypeImpl(componentType);
                        }
                    }

                    @Override
                    Type usedInGenericType(Type type)
                    {
                        return checkNotNull(type);
                    }
                },
        JAVA8
                {
                    @Override
                    Type newArrayType(Type componentType)
                    {
                        return JAVA7.newArrayType(componentType);
                    }

                    @Override
                    Type usedInGenericType(Type type)
                    {
                        return JAVA7.usedInGenericType(type);
                    }

                    @Override
                    String typeName(Type type)
                    {
                        try
                        {
                            Method getTypeName = Type.class.getMethod("getTypeName");
                            return (String) getTypeName.invoke(type);
                        }
                        catch (NoSuchMethodException e)
                        {
                            throw new AssertionError("Type.getTypeName should be available in Java 8");
                            /*
                             * Do not merge the 2 catch blocks below. javac would infer a type of
                             * ReflectiveOperationException, which Animal Sniffer would reject. (Old versions of
                             * Android don't *seem* to mind, but there might be edge cases of which we're unaware.)
                             */
                        }
                        catch (InvocationTargetException e)
                        {
                            throw new RuntimeException(e);
                        }
                        catch (IllegalAccessException e)
                        {
                            throw new RuntimeException(e);
                        }
                    }
                },
        JAVA9
                {
                    @Override
                    Type newArrayType(Type componentType)
                    {
                        return JAVA8.newArrayType(componentType);
                    }

                    @Override
                    Type usedInGenericType(Type type)
                    {
                        return JAVA8.usedInGenericType(type);
                    }

                    @Override
                    String typeName(Type type)
                    {
                        return JAVA8.typeName(type);
                    }

                    @Override
                    boolean jdkTypeDuplicatesOwnerName()
                    {
                        return false;
                    }
                };

        static final JavaVersion CURRENT;

        static
        {
            if (AnnotatedElement.class.isAssignableFrom(TypeVariable.class))
            {
                if (new TypeCapture<Entry<String, int[][]>>()
                {
                }.capture()
                        .toString()
                        .contains("java.util.Map.java.util.Map"))
                {
                    CURRENT = JAVA8;
                }
                else
                {
                    CURRENT = JAVA9;
                }
            }
            else if (new TypeCapture<int[]>()
            {
            }.capture() instanceof Class)
            {
                CURRENT = JAVA7;
            }
            else
            {
                CURRENT = JAVA6;
            }
        }

        abstract Type newArrayType(Type componentType);

        abstract Type usedInGenericType(Type type);

        final ImmutableList<Type> usedInGenericType(Type[] types)
        {
            ImmutableList.Builder<Type> builder = ImmutableList.builder();
            for (Type type : types)
            {
                builder.add(usedInGenericType(type));
            }
            return builder.build();
        }

        String typeName(Type type)
        {
            return Types.toString(type);
        }

        boolean jdkTypeDuplicatesOwnerName()
        {
            return true;
        }
    }

    /**
     * Per <a href="https://code.google.com/p/guava-libraries/issues/detail?id=1635">issue 1635</a>,
     * In JDK 1.7.0_51-b13, {@link TypeVariableImpl#equals(Object)} is changed to no longer be equal
     * to custom TypeVariable implementations. As a result, we need to make sure our TypeVariable
     * implementation respects symmetry. Moreover, we don't want to reconstruct a native type variable
     * {@code <A>} using our implementation unless some of its bounds have changed in resolution. This
     * avoids creating unequal TypeVariable implementation unnecessarily. When the bounds do change,
     * however, it's fine for the synthetic TypeVariable to be unequal to any native TypeVariable
     * anyway.
     */
    static final class NativeTypeVariableEquals<X>
    {
        static final boolean NATIVE_TYPE_VARIABLE_ONLY =
                !NativeTypeVariableEquals.class.getTypeParameters()[0].equals(
                        newArtificialTypeVariable(NativeTypeVariableEquals.class, "X"));
    }

    private Types()
    {
    }
}
